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In this work, we have studied the spin dynamics of a synthetic antiferromagnet (AFM)/heavy metal/ferromagnet double barrier magnetic tunnel junction in the presence of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, interfacial Dzyaloshinskii–Moriya (iDM) interaction, Néel field, and Spin–Orbit Coupling (SOC) with different Spin-Transfer Torque (STT). We employ the Landau–Lifshitz–Gilbert–Slonczewski equation to investigate the AFM dynamics of the proposed system. We found that the system exhibits a transition from regular to damped oscillations with the increase in strength of STT for systems with a weaker strength of iDM interaction than RKKY interaction while displaying sustained oscillations for systems having the same order of RKKY and iDM interactions. On the other hand, the systems with sufficiently strong iDM interaction strength exhibit self-similar but aperiodic patterns in the absence of the Néel field. In the presence of the Néel field, the RKKY interaction dominating systems exhibit chaotic oscillations for low STT but display sustained oscillations under moderate STT. Our results suggest that the decay time of oscillations can be controlled via SOC. The system can work as an oscillator for low SOC but displays non-linear characteristics with the rise in SOC for systems having weaker iDM interaction than RKKY interactions. In contrast, opposite characteristics are noticed for iDM interaction dominating systems. We found periodic oscillations under low external magnetic fields in RKKY interaction dominating systems. However, moderate fields are necessary for sustained oscillation in iDM interaction dominating systems. Moreover, the system exhibits saddle-node bifurcations and chaos under moderate Néel field and SOC with suitable RKKY and iDM interactions. In addition, our results indicate that the magnon lifetime can be enhanced by increasing the strength of iDM interaction for both optical and acoustic modes. [ABSTRACT FROM AUTHOR]

The type-II Dirac fermions are characterized by a tilted Dirac cone and sustain exotic quantum transport phenomena. Here, we show the emergence of a type-II Dirac nodal loop in the SrVO 3 / SrTiO 3 quantum well structure by density functional theory calculations and symmetry arguments. When the spin–orbit coupling (SOC) is neglected, the unavoidable crossing between two t 2 g bands gives rise to a nodal loop in the Brillouin zone, which is protected by the mirror symmetry. Such a nodal loop is fully gapped by including SOC, which results in a large spin Hall effect due to large spin Berry curvatures. Our findings add the unexplored functionality to oxide quantum wells and offer a practical platform to explore the interplay between topological fermions and spin transport phenomena. [ABSTRACT FROM AUTHOR]

The second-order nonlinear Hall effect in 8-Pmmn monolayer borophene under the influence of an out-of-plane electric field and intrinsic spin–orbit interaction is reported. This unconventional response sensitive to the breaking of discrete and crystal symmetries can be tuned by the applied electric field, which can vary the bandgap induced by spin–orbit coupling. It is described by a Hall conductivity tensor that depends quadratically on the applied electric field. We find that the nonlinear Hall effect strongly depends on the spin polarization. In particular, it exhibits out of the phase character for spin-up and spin-down states. Remarkably, it undergoes a phase flip in the spin-up state at a large out-of-plane electric field that generates a staggered sublattice potential greater than the spin–orbit interaction strength. It is shown that the nonlinear Hall effect in the system originates from the broken inversion symmetry that plays an indispensable role in developing finite Berry curvature and its relevant dipole moment. It is found that at zero temperature, the nonlinear Hall response is maximal when the Fermi energy is twice the bandgap parameter and vanishes at large Fermi energies. Notably, the peak of nonlinear Hall response shifts to lower Fermi energies at finite temperature. [ABSTRACT FROM AUTHOR]

Some spinel chromium oxides with the chemical formula ACr2O4 exhibit magnetic-induced multiferroicity due to the special spiral spin order. However, because of the relatively low temperature of the ordered spiral phase, this kind of multiferroicity generally displays a limited coexistence of magnetic and ferroelectric orders in a narrow temperature range. The Jahn–Teller (JT) effect, serving as a crucial link between charge and orbit degrees of freedom, can facilitate efficient modulation of multiferroic properties. In this work, Ni1−xCuxCr2O4 (0 ≤ x ≤ 0.2) series are synthesized by occupying the same Wyckoff site with two kinds of JT ions. The microstructure and JT distortion can be distinctly influenced by varying the doping level of Cu2+ ions. Particularly, Ni0.85Cu0.15Cr2O4 (x = 0.15) presents the pronounced JT distortion, accompanied by observation of dielectric anomaly at ∼78 K, resulting from spin–orbit coupling. This implies that the JT effect can significantly promote the contribution of spin–orbit coupling in magnetoelectric correlation. Moreover, the magnetodielectric effect induced by intrinsic magnetoelectric coupling is confirmed in Ni0.85Cu0.15Cr2O4 over a wide temperature range of 10–200 K, which is much higher than the Néel temperature of ∼85 K. It indicates that spin–orbit coupling based on the JT effect could overcome the constraint of magnetic order to achieve effective control on electric polarization performance under an applied magnetic field, thereby showing broad application prospects. [ABSTRACT FROM AUTHOR]

Investigating the interplay between charge and spin conversion in two-dimensional (2D) materials holds significant promise for futuristic electronic applications. Through density functional theory, our study delves into the charge-spin conversion and spin density dynamics in the non-magnetic SnNBr monolayer under time-reversal invariance. The breaking of out-of-plane mirror symmetry and inversion symmetry, along with the presence of spin–orbit coupling (SOC) lead to a notable momentum-dependent spin band splitting or Rashba effect induced by the inherent out-of-plane electric field. Theoretical calculations reveal not only the presence of profound Rashba spin splitting but also the coexistence of intrinsic spin Hall effects in the SnNBr monolayer. Analysis of k-resolved spin Berry curvature sheds light on the origin of the substantial intrinsic spin Hall conductivity. Furthermore, our research highlights the modulation of charge-to-spin conversion and spin density accumulation through in-plane biaxial strains. Moreover, the variation in the Rashba parameter is correlated with the changes in the built-in out-of-plane electric field and microscopic atomic orbital contributions. These findings underscore the exceptional potential of the non-centrosymmetric SnNBr monolayer for advanced spintronics, spin-orbitronics, and piezo-spintronic applications, and serve as a catalyst for further experimental investigations. [ABSTRACT FROM AUTHOR]

The Rashba spin–orbit coupling effect, primarily arising from structural-inversion asymmetry in periodic crystals, has garnered considerable attention due to its tunability and potential applications in spintronics. Its capability to manipulate electron spin without an external magnetic field opens new avenues for spintronic device design, particularly in semiconductor technology. Within this framework, 2D Rashba materials hold special interest due to their inherent characteristics, which facilitate miniaturization and engineering capabilities. In this Perspective article, we provide an overview of recent advancements in the research of 2D Rashba materials, aiming to offer a comprehensive understanding of the diverse manifestations and multifaceted implications of the Rashba effect in material science. Rather than merely presenting a list of materials, our approach involves synthesizing various viewpoints, assessing current trends, and addressing challenges within the field. Our objective is to bridge the gap between fundamental research and practical applications by correlating each material with the necessary advancements required to translate theoretical concepts into tangible technologies. Furthermore, we highlight promising avenues for future research and development, drawing from insights gleaned from the current state of the field. [ABSTRACT FROM AUTHOR]

In recent years, magnetic skyrmion-based spin-torque nano-oscillators (STNOs) have attracted considerable interest for their prospect in future-generation communication and spintronic technologies. However, some critical issues, which hamper their practical applications, e.g., the long start-up time and variable skyrmion gyration orbit, remain to be resolved. Here, we numerically demonstrate the realization of a fixed-orbit STNO, which is based on an interlayer-coupled meron–skyrmion (MS) pair instead of a magnetic skyrmion. In this STNO, the MS pair possesses a structurally defined, fixed orbit within a broad range of driving currents, even in the presence of random defects. The output frequency range of the STNO based on an MS pair far exceeds that of the STNO typically featuring a single skyrmion. Moreover, the output frequency of this STNO can be further elevated if more MS pairs are incorporated. Our results reveal the nontrivial dynamics of the interlayer-coupled MS pair, opening perspectives for the design and optimization of fundamental spintronic devices. [ABSTRACT FROM AUTHOR]

We investigate the native point defects in the long-wavelength infrared (LWIR) detector material H g 0.75 C d 0.25 Te using a dielectric-dependent hybrid density functional combined with spin–orbit coupling. Characterizing these point defects is essential as they are responsible for intrinsic doping and nonradiative recombination centers in the detector material. The dielectric-dependent hybrid functional allows for an accurate description of the bandgap (E g) for Hg 1 − x Cd x Te (MCT) over the entire compositional range, a level of accuracy challenging with standard hybrid functionals. Our comprehensive examination of the native point defects confirms that cation vacancies V Hg (Cd) are the primary sources of p -type conductivity in the LWIR material given their low defect formation energies and the presence of a shallow acceptor level (− /0) near the valence-band maximum. In addition to the shallow acceptor level, the cation vacancies exhibit a deep charge transition level (2 − / −) situated near the midgap, characteristic of nonradiative recombination centers. Our results indicate that Hg interstitial could also be a deep center in the LWIR MCT through a metastable configuration under the Hg-rich growth conditions. While an isolated Te antisite does not show deep levels, the formation of V Hg –Te Hg defect complex introduces a deep acceptor level within the bandgap. [ABSTRACT FROM AUTHOR]

The combined influence of spin–orbit coupling and spatial inversion asymmetry leads to an enhancement of electronic properties, including Rashba spin-splittings as well as spin Hall effect. Recent research has shown the possibility to create two-dimensional Janus materials with inherent structural asymmetry. In this work, the structural stability, piezoelectricity, electronic properties, and intrinsic spin Hall conductivity of quintuple-layer atomic Janus Sb2XSX' (X, X' = S, Se, Te; X ≠ X') monolayers are investigated using first-principles calculations within the framework of density functional theory. They demonstrate relatively high in-plane piezoelectric coefficients ( d 22) and also possess out-of-plane piezoelectric coefficients ( d 31), which is due to the breaking of inversion symmetry in the crystal structure with the space group P3m1. Large Rashba parameters are obtained in Janus Sb2XSX' monolayers, especially high for Sb 2 S 2 Te (1.62 eV Å) and Sb 2 SeSTe (1.33 eV Å) due to strong spin–orbit coupling. Moreover, Rashba-like spin-splitting is also observed in the edge-states as well, which is highest for Sb 2 SeSTe with 2.17 eV Å. Furthermore, Sb 2 S 2 Te and Sb 2 SeSTe monolayers reveal a significantly high Berry curvature (65.59 and 61.05 Bohr 2), spin Berry curvature (− 118.4 and − 120.6 Bohr 2), and spin Hall conductivity (1.8 and 1.6 e 2 /h). Our results suggest that Janus Sb 2 S 2 Te and Sb 2 SeSTe monolayers could be an excellent platform for multifunctional electronic applications. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) demonstrate a broad spectrum of properties encompassing electronic correlations, anisotropic transport, magnetism, and optical behavior. The anisotropy arises from both intrinsic crystal symmetry and extrinsic factors like epitaxial strain and structural asymmetry at TMO interfaces. Weiss and Neel's work has elucidated anisotropic magnetic behavior in antiferromagnetic (AFM) materials. AFM TMOs exhibit unique magnetotransport behavior, including weak antilocalization (WAL) and anisotropic magnetoresistance (AMR). Understanding the magnetic structure and band topology in AFM perovskites and their interfaces enables the tailored design of materials for spintronics and energy conversion. In few interfaces lacking inversion symmetry, Rashba spin–orbit coupling (SOC) induces WAL, a quantum correction in conductivity in a two-dimensional electronic system. Electron accumulation and charge transfer across 3d, 5d transition metal-based perovskite interfaces affect WAL and AMR, as observed in 3d/3d and 3d/5d AFM heterostructures, respectively. Advancements in spintronics rely on exploring spin-dependent transport anisotropy. This review focuses on various scattering mechanisms, categorized as extrinsic and intrinsic, in anisotropic transport, particularly in 3d/5d AFM superlattices. The WAL scattering mechanism depends on both intrinsic factors related to Rashba SOC-induced band topology and extrinsic sources like spin impurities and lattice ions. Moreover, the investigation into AMR mechanisms involves the application of impurity-based extrinsic scattering models, which are aligned with the Rashba and Dresselhauss models on Fermi surfaces. This exploration specifically targets the interface of two-band insulators, exemplified by LaAlO3/SrTiO3 and LaVO3/KTaO3. Furthermore, this model achieves comprehensive coverage, extending its applicability to 3d/5d AFM heterostructures like LaMnO3/SrIrO3 and CaMnO3/CaIrO3. Additionally, the intrinsic scattering mechanism tied to Berry phase effects related to band topology is studied, focusing on the CaMnO3/CaIrO3 superlattice. Despite manipulation challenges stemming from reduced stray fields, AFM materials show potential in interface physics and applications within the realm of spintronics. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) piezoelectric nanomaterials have widely been studied recently due to their promise for various applications in technology. Investigation of vertical piezoelectricity will contribute to a deeper understanding of the intrinsic mechanism of piezoelectric effects in the 2D structures. In this paper, we report a first-principle study for the structural, electronic, piezoelectric, and transport properties of new-designed Janus WSi Z 3 H (Z = N, P, and As) monolayers. The structural stability of WSi Z 3 H is theoretically confirmed based on the energetic, phonon dispersion, and also elastic analyses. At the ground state, while WSiN 3 H is an indirect semiconductor, both WSiP 3 H and WSiAs 3 H are predicted to be direct semiconductors with smaller bandgaps. When the spin-orbit coupling effects are taken into account, a large valley spin splitting is observed at the K point of WSi Z 3 H materials. Interestingly, a giant Rashba spin splitting is found in WSiP 3 H and WSiAs 3 H with Rashba constant α R up to 770.91 meV Å. Additionally, our first-principles study indicates that Janus WSi Z 3 H monolayers are piezoelectric semiconductors with high out-of-plane piezoelectric coefficient | d 31 | , up to 0.15 pm/V, due to the broken mirror symmetry. Besides, with high electron mobilities and also possessing direct band gaps, WSiP 3 H and WSiAs 3 H monolayers are favorable for applications in optoelectronics. [ABSTRACT FROM AUTHOR]

Spin–orbit torque provides an efficient strategy for electric manipulation of magnetization. However, Joule heat accompanying with electron motion in the electron-mediated spin current result in unavoidable power dissipation. Moreover, the spin diffusion length in electron-mediated spin current is relatively short, preventing the transmission of spin information over long distances. Magnon-mediated spin current, without moving electrons, can be an excellent alternative to the conventional spin current. Magnon-mediated transfer torque effect has been reported in several previous works. Here, we report the magnon-mediated spin Hall magnetoresistance (SMR) and unidirectional magnetoresistance (UMR) in Pt/NiO/NiFe structures. The significant SMR and UMR were observed in the samples with the NiO thickness up to 60 nm, demonstrating the efficient transmission of magnon-mediated spin current over long distances in the NiO layer. In addition, we observed current-induced in-plane magnetization switching in the NiFe layer via the UMR measurement. These results demonstrated the possibility for developing the efficient spintronic devices operated by magnons. [ABSTRACT FROM AUTHOR]

In this work, we have studied the spin-dependent ballistic transport and anomalous quantum tunneling in bilayer graphene horizontally placed in between two Rashba–Zeeman (RZ) leads under external electric biasing. We investigated the transmission and conductance for the proposed system using scattering matrix formalism and the Landauer–Büttiker formula considering a double delta-like barrier under a set of experimentally viable parameters. We found that the transmission characteristics are notably different for up- and down-spin incoming electrons depending upon the strength of magnetization. Moreover, the transmission of up- and down-spin electrons is found to be magnetization orientation dependent. The maximum tunneling conductance can be achieved by tuning biasing energy and magnetization strength and choosing a material with suitable Rashba spin–orbit coupling (RSOC). This astonishing property of our system can be utilized in fabricating devices, such as spin filters. We found that the Fano factor of our system is 0.4 under strong magnetization conditions, while it reduces to 0.3 under low magnetization conditions. Moreover, we also noticed that the transmission and conductance significantly depend on the Rashba–Zeeman effect. Therefore, considering a suitable RZ material, the tunneling of the electrons can be tuned and controlled. Our result suggests that considering suitable strength and orientation of magnetization with moderate RSOC, one can obtain a different transmission probability for spin species under suitable biasing energy. These results indicate the suitability of the proposed system in fabrication of spintronic devices, such as spin filter, spin transistor, etc. [ABSTRACT FROM AUTHOR]

Antiferromagnetic spintronics is intrigued due to its unique properties that could break through the restrictions in ferromagnets. A 3d/5d transition metal oxide heterostructure is a good platform in antiferromagnetic spintronics research since the strong spin–orbit coupling in 5d oxides may bring about delicate interaction with the correlation energy and motivate unconventional phenomena. Here, the transport and magnetic characters of bilayers composed of antiferromagnetic 3d perovskite NdNiO3 and 5d perovskite SrIrO3 were investigated. The decreased metal–insulator transition and Néel temperature associated with suppressed negative magnetoresistance, emerged spin-glass like phenomenon, and the humped nonlinear Hall effect were observed in NdNiO3/SrIrO3 bilayers, which were absent in NdNiO3 and SrIrO3 pure films. It suggests the important role of interfacial interaction between NdNiO3 and SrIrO3 in modulating heterostructure transport and magnetic behavior and also manifests that complex magnetic structures might be realized in NdNiO3/SrIrO3 bilayers. [ABSTRACT FROM AUTHOR]

In this paper, we examined the effects of proximity-induced interactions such as Rashba spin-orbit coupling and effective Zeeman fields (EZFs) on the optical spectrum of n -type and p -type monolayer (ML)-MoS 2. The optical conductivity is evaluated using the standard Kubo formula under random-phase approximation by including the effective electron–electron interaction. It has been found that there exist two absorption peaks in n -type ML-MoS 2 and two knife shaped absorptions in p -type ML-MoS 2 , which are contributed by the inter-subband spin-flip electronic transitions within conduction and valence bands at valleys K and K ′ with a lifted valley degeneracy. The optical absorptions in n -type and p -type ML-MoS 2 occur in THz and infrared radiation regimes and the position, height, and shape of them can be effectively tuned by Rashba parameter, EZF parameters, and carrier density. The interesting theoretical predictions in this study would be helpful for the experimental observation of the optical absorption in infrared to THz bandwidths contributed by inter-subband spin-flip electronic transitions in a lifted valley degeneracy monolayer transition metal dichalcogenides system. The obtained results indicate that ML-MoS 2 with the platform of proximity interactions make it a promising infrared and THz material for optics and optoelectronics. [ABSTRACT FROM AUTHOR]

The recent discovery of inherently stable two-dimensional (2D) transition-metal dichalcogenides (TMDs) provides a unique platform for spintronic devices. However, its efficacy for electric detection by spin Hall magnetoresistance (SMR) has not been established yet. In this work, we report on SMR in 2D TMDs/ferromagnet heterostructures, i.e., PtSe 2 /NiFe (Py), whose magnitude reaches the maximum with bilayer PtSe 2. Notably, the SMR value in bilayer PtSe 2 /Py heterostructures undergoes a sign change with increasing Py thickness. For thinner Py samples, the SMR rapidly decreases with increasing Py thickness, eventually changing from positive to negative. In the case of intermediate Py thicknesses, the SMR consistently exhibits negative behavior. However, for thicker Py samples, the negative SMR values gradually decrease. This complex behavior is attributed to the dominant and competing mechanisms that contribute to SMR, including the spin Hall effect (or Rashba-induced effect) and its inverse effect, the orbital Hall effect and its inverse effect, as well as interfacial spin–orbit-coupling-induced spin-current-to-charge-current conversion. These findings would expand the arsenal for advanced spintronic applications based on 2D TMDs. [ABSTRACT FROM AUTHOR]

Motivated by the booming development of spintronics based on chiral helical microstructures, we employed the standard nonequilibrium Green's function theory to study nonreciprocity and chirality of the heat generation and spin filtering in ferromagnetic helical chains. Our results demonstrate that magnetization, spin–orbit interaction, and nonstep electrostatic potential distribution by bias jointly determine nonreciprocity of the heat generation, and only spin–orbit interaction determines nonreciprocity of the spin-polarized current. Chirality of the heat generation and spin-polarized current is determined by both magnetization and spin–orbit interaction, and some quantitative relationships related to chirality were discovered. However, a transverse field can break these relations and suppress heat generation significantly and modulate nonreciprocity and chirality of the spin-polarized current effectively. By further simulating the critical electrostatic potential distribution, we found with the transverse field applied, compared to the case with zero temperature, that the finite temperature less than one characteristic phonon energy can suppress nonreciprocity of the heat generation while enhancing that of the spin filtering. In terms of chirality, compared to the left-handed helical structure, the right-handed one is more advantageous for designing spin filtering diodes. [ABSTRACT FROM AUTHOR]

In order to explore the interplay among heat, charge, and spin, we investigate the spin-related thermoelectricity of a hybrid double quantum dot Aharonov–Bohm interferometer with Rashba spin–orbit coupling (RSOC). Interestingly, the nonzero RSOC phase difference can induce significant spin-dependent thermoelectric transport. Not only can the strong violation of the Wiedemann-Franz law be obtained, but also a pure spin-Seebeck effect can be produced, which may serve as a pure spin-current generator. The influence of system parameters on thermoelectric coefficients (especially for spin counterparts) are analyzed in detail, and the underlying physics is further elucidated. Furthermore, the spin figure of merit can be much larger than the charge one, which, thus, provides a realistic possibility of engineering spin thermoelectric devices with high performance. These results obtained may be of interest for developing spin thermoelectric devices in the field of spin caloritronics. [ABSTRACT FROM AUTHOR]

This Tutorial article focuses on magnetic phenomena and material systems that have gained significant importance since the original development of mumax3, but are challenging to simulate for users who rely solely on the originally provided examples. Alongside the physical background, we provide hands-on examples of advanced magnetic systems, including detailed explanations of complete mumax3 input files (13 in total, often showing different ways to achieve things), and highlighting potential pitfalls where applicable. Specifically, we explore two approaches to incorporate spin–orbit torques in mumax simulations, considering the trade-off between versatility and speed. We also examine complex multilayer material stacks, including synthetic antiferromagnets, demonstrating different implementation methods that again vary in speed, versatility, and realism. A key criterion for selecting the optimal simulation strategy is its suitability for modeling systems where the magnetization varies significantly in the third dimension. The material covered in this Tutorial paper includes content developed for the mumax3 workshop presented during the summer of 2020 within the context of the IEEE online spintronics seminar, along with additional new topics. Throughout the explanations, we ensure broad applicability beyond specific examples. [ABSTRACT FROM AUTHOR]

The manipulation of spin–orbit torque (SOT) manifests enormous potentiality in the field of spintronics due to virtues of low power consumption, ultrafast spin-flips, and high-density integration. Increaser the spin hall angle of the spin source layer or the SOT efficiency are the key approaches of achieving low power spintronics. Here, we report an enhancement of spin–orbit torques in Ta/Co/Pt heterostructures using low-voltage ionic liquid gating. The effective spin Hall angle increased threefold with an applied voltage of 2 V. As expected, the enhanced spin Hall angle lowers the critical current density by 66.7% (1.14 × 107 to 3.80 × 106 A cm−2). By the lock-in harmonic Hall voltage measurements, the outstanding performance of manipulation of the spin–orbit coupling originates from the electrostatic doping interracially by the ionic liquid. In addition to the significant fundamentals, our work could be feasibly wielded toward the spintronics such as memory and logic devices in the behaviors of energy-efficient and impressive tunability. [ABSTRACT FROM AUTHOR]

Reliability and packing density concerns are the two major shortcomings of spin transfer torque and spin orbit torque based magnetic memory, respectively. Voltage controlled magnetic anisotropy (VCMA) becomes energy efficient and fast, showing transcendence for the writing mechanism in the magnetic tunnel junction. Deterministic switching cannot be achieved by VCMA alone in the out of plane nanomagnet. It requires an external in-plane magnetic field, but the use of an external field is inconvenient for on-chip applications. We exploit stress and exchange bias provided by an antiferromagnetic material to mitigate the external magnetic field requisite. We perform macro-spin simulations using the Landau–Lifshitz–Gilbert equation at room temperature. We use the VCMA effect cum stress effect to investigate field free switching performance, and this improves the write error rate (WER) to 5 × 10 − 5 against WER of 0.1 with the VCMA effect alone. We studied the effects of applied voltage (amplitude and pulse width), exchange bias field, and VCMA coefficient on the switching performance in detail. This proposed two-terminal device can be helpful in achieving high cell density to implement nonvolatile magnetic memory. [ABSTRACT FROM AUTHOR]

We present a simplified tight-binding (TB) model to describe the low-energy physics of monolayer 1T' transition metal dichalcogenides (TMDCs). The TB model is constructed by combining symmetry analysis and first-principle calculations. Our TB model accurately reproduces the electronic structures near the Fermi energy and provides a better representation of energy band inversion. By considering spin–orbit coupling (SOC), our TB model successfully reproduces the opening of the bandgap, characterizes nontrivial topology, and predicts corresponding helical edge states. Additionally, using this TB model, we observe that quantized electronic conductance remains robust under significant disorder intensity. However, the robustness of the edge states can be suppressed by the Zeeman fields and SOC strength in the scattering zone. Furthermore, moderate concentrations of vacancy disorder destroy the topological protection and eliminate quantized conductance. Our TB model serves as a starting point for a comprehensive understanding of the properties of these materials and can guide future research on superconductivity, strain, and correlation effects. [ABSTRACT FROM AUTHOR]

In this work, we study the electronic properties of nanotubes with spin–orbit interaction that exhibit a spin Hall effect. Nanoribbons made of these materials are expected to have topologically protected states. The lack of edge states in a seamless tube eliminates the possibility of finding a topological edge state. The spin–orbit interaction breaks the degeneracy of Dirac's cones and eliminates the chance of finding a metal nanotube. As a consequence, this makes all nanotubes with spin–orbit interaction trivial band insulators. We focus our attention on two features. First, we study the energy band gap as a function of the diameter of the nanotubes. Then, we concentrate on controlling the bandgap of a nanotube by applying an external radial electric field. Finally, we discuss the possibility of using one of these tubes as a field-effect transistor. [ABSTRACT FROM AUTHOR]

Low-dimensional materials with topologically protected edge states have wide applications in spintronic, valleytronic, and optoelectronic nanodevices. Different from the valley-resolved quantum anomalous Hall (VQAH) state and spin-polarized quantum anomalous Hall (VSQAH), the photon-induced topological states in kagome-lattice nanoribbons (KLNR) can generate both valley and spin-polarized edge states without magnetic substrate or Rashba spin-orbit coupling (SOC). Via the Floquet theory, we also propose a 0-photon-extraction scheme to obtain the effective Hamiltonian under low-frequency light for the first time, and we analyze the topological properties and phase transition of the irradiated kagome system, similar with those in the high-frequency case. We then design an all-optically controlled valley-resolved spin filter based on KLNR. Transmissions and local current distributions of the proposed nanodevice confirm this spin-filter effect, which can indeed be switched by left- or right-circularly-polarized (LCP/RCP) light. We believe these optically controlled models can be extended to the design of magnetism-free spin-valley filter or switcher in the future. [ABSTRACT FROM AUTHOR]

In this Perspective, we present some important aspects of two fundamental concepts of modern spintronics, namely, spin–orbit torque and topology. Although these two fields emerged separately in condensed matter physics, in spintronics they show a deep connection, which requires further theoretical and experimental investigation. The topological features can arise both from momentum space via the wave functions as well as from real space via complex magnetic configurations. These features manifest themselves as unique aspects of different equilibrium and non-equilibrium properties. Physical interactions of such a topological origin can open new possibilities for more efficient mechanisms for manipulating magnetic order with electrical currents, which, in turn, can lead to faster and more efficient spintronics devices. [ABSTRACT FROM AUTHOR]

We study the W/Cu multilayers as a spin current source and the coherent spin–orbit torques in a Fe layer using the spin-torque ferromagnetic resonance (STFMR) technique. With increasing numbers of layers, the line shape of the STFMR signals changes from predominantly antisymmetric to predominantly symmetric. When using [W(0.5)/Cu(0.5)]5 as a spin current source, the symmetric amplitude increases by a factor of 5 compared to a single W layer. Simultaneously, the effective damping parameter also increases slightly due to enhanced spin pumping. Along with an increasing trend in the damping-like torque efficiency, this suggests that the extrinsic spin Hall effect is enhanced. Concurrently, the antisymmetric amplitude decreases significantly by a factor of 27, which indicates an increase in the field-like torque when multilayers are used as a spin current source. [ABSTRACT FROM AUTHOR]

Density functional theory calculations are performed to systematically investigate the electronic and magnetic properties of few-layer and bulk Fe3SiSe2 (FSS). We predict that the bulk FSS has a metallic ground state and a layered structure displaying intralayer ferromagnetic ordering and interlayer antiferromagnetic ordering. The itinerant magnetism in the FSS was determined by the Stoner criterion. Predictions of the absence of unstable phonon modes and a moderate cleavage energy of only 28.3 meV/Å2 suggest the possibility of stabilizing FSS in a monolayer form. The calculated spin–orbit coupling facilitates not only a large magnetocrystalline anisotropy energy, around 500 μeV/Fe, but also spontaneous valley polarization in odd-numbered layer systems. These systems have net magnetic moments as the magnetic moments of AFM-ordered layers are not fully compensated in the odd-numbered layer case and are predicted to show 2D metallic behaviors. The magnitude of the valley polarization in odd-numbered layered systems decreases from 18 meV with layer number but is absent in even-layered structures, thus showing an odd–even oscillation effect. Experimental realization of this bidimensional metallic magnet is, therefore, expected to widen the arena of two-dimensional materials that show exotic phenomena. [ABSTRACT FROM AUTHOR]

Transmission electron microscope image and electronic transport of La0.7Sr0.3MnO3 (LSMO) films grown on (001) oriented Si using the sputtered pulsed plasma method confirmed the presence of around 8 nm thick, less dense, and highly resistive LSMO at the interface below the conducting phase. Thicker LSMO films, in addition to metal-insulator transition, show an anomaly around the Curie temperature in temperature-dependent resistivity and magnetoresistance (MR), which is a unique observation. The conduction in these LSMO films at temperatures below low-temperature resistivity minimum is dominated by Kondo-like scattering over electron–electron scattering, established using the phenomenological model. At 20 K, the maximum positive MR is ∼ 12% for the in-plane field, while it is ∼ 7.2% for the out-of-plane field. The maximum negative in-plane MR is found to be ∼ 42.5%, which becomes ∼ 30% when the orientation of the field changes to the out-of-plane direction. The two-dimensional field-dependent change in the magneto-conductance model evidenced the quantum interference effect (QIE). The existence of QIE is associated with magnetic scattering and scattering due to spin–orbit coupling. These results may be used to modulate the electrical properties of future electronic devices and can encourage scientists to explore the multi-functionalities of complex oxides grown on bare Si substrates. [ABSTRACT FROM AUTHOR]

The field-free spin–orbit torque induced 180° reorientation of magnetization is beneficial for the high performance magnetic memory. The antiferromagnetic material (AFM) can provide a higher operation speed than the ferromagnetic counterpart. In this paper, we propose a trilayer AFM/insulator/heavy metal structure as the AFM memory device. We show that the field-free switching of the AFM with a perpendicular Néel vector can be achieved by using two orthogonal currents, which provide a uniform damping-like torque and uniform field-like torque, respectively. The reversible switching can be obtained by reversing either current. A current density of 1.79 × 1011 A/m2 is sufficient to induce the switching. In addition, the two magnetic moments become noncollinear during switching. This enables an ultrafast switching within 40 ps. The device and switching mechanism proposed in this work offer a promising approach to deterministically switch the AFM with the perpendicular Néel vector. It can also stimulate the development of an ultrafast AFM-based MRAM. [ABSTRACT FROM AUTHOR]

A giant magnetoresistance (GMR) sensor with a Wheatstone bridge structure and an out-of-plane linear response was developed. The spin-valve structure consists of a synthetic antiferromagnetic [(Co/Pt)n/Ru/(Pt/Co)n] reference layer with perpendicular magnetic anisotropy, a Cu spacer layer, and a Co-free layer with in-plane easy magnetization. By utilizing the spin–orbit torque induced magnetization switching in the synthetic antiferromagnetic layer, the magnetization of the reference layers in the adjacent bridge arms is set to the opposite direction, achieving a GMR sensor with a full Wheatstone bridge structure. The sensor exhibits linear response to the out-of-plane magnetic field with adjustable dynamic ranges from hundreds to thousands of Oe, depending on the thickness of the Co-free layer. A similar Wheatstone bridge sensor consisting of magnetic tunnel junctions was also proposed. The sensor with out-of-plane linear response may have promising applications in three-dimensional magnetic field detection and current sensing field. [ABSTRACT FROM AUTHOR]

In this study, we prepared a multi-layer Tb–Fe/Pt/Tb–Fe wire to develop a multi-level magnetic memory. By applying current, magnetizations of the Tb–Fe layers were inversion symmetrically switched by spin– orbit torque (SOT) generated from the middle Pt layer. Measurements of SOT showed that its efficiency had opposite polarities in the top and bottom Tb–Fe layers. The switching current density of the top and bottom Tb–Fe layers shifted in opposite directions under a uniform perpendicular magnetic field. Because the perpendicular magnetic field broke the inversion symmetry of SOT generated from the middle Pt layer, it could be used to control the switching current. Our results prove that the additional uniform and perpendicular magnetic field can enhance the controllability of the magnetization state in case of multi-level SOT-induced magnetization switching. [ABSTRACT FROM AUTHOR]

Graphyne has recently attracted much attention since it is an important derivative of graphene with unique topological properties. Although graphyne is not a conventional topological insulator because of its weak spin–orbit coupling, it is a real Chern topological insulator with the higher-order topology. However, it lacks a realistic model. Here, we propose a schedule to realize acoustic graphyne. By introducing negative coupling to simulate the carbon–carbon triple bond, we realize the transition from trivial to higher-order topological phases, characterized by real Chern numbers. These topologically protected corner states are achieved in a finite-size sample, and the condition for their existence is discussed. Our research extends the concept of real Chern insulators and provides a platform for studying the topological properties of graphene-like structural compounds. [ABSTRACT FROM AUTHOR]

In this work, thin films of ruthenium-doped and cerium-doped yttrium iron garnet were deposited on silicon using solgel chemistry. Doped YIG could be produced in phase pure form up to a precursor stoichiometry of Y3Ru0.1Fe4.9O12 and Ce0.7Y2.3Fe5O12. Both dopants significantly increase the coercivity and anisotropy field of the materials either due to domain wall pinning or increased spin–orbit coupling from the dopant. To delineate these two effects, the dynamic magnetic properties were studied using strip line ferromagnetic resonance (FMR). The FMR linewidth was separated into intrinsic loss and inhomogeneous line broadening. Inhomogeneous line broadening was found to dominate the magnetic losses in all the films likely due to magnon scattering off grain boundaries, but the Gilbert damping remained fairly low. By comparing the two dopants, it was found that Gilbert damping increased more in Ce:YIG films than in Ru:YIG films. This finding was corroborated by changes in the anisotropy field of the films, indicating a larger contribution from spin–orbit coupling from cerium than from ruthenium. Surprisingly, while magnetic loss globally increased with higher substitution, adding a small amount of dopant actually reduced the inhomogeneous line broadening in both sets of films. This was corroborated by crystallite size. The damping in Ru:YIG also decreased with a small amount of the dopant, which has been predicted by Kittel for doped garnets. Thus, it follows that there is an ideal doping regime where solgel YIG can be doped at low levels without increasing magnetic loss. [ABSTRACT FROM AUTHOR]

We present femtosecond-pulse-induced precession of magnetization at low laser fluence (< 5 μ J / cm 2) regime as a function of magnetic field and laser fluence in three Co/Pd multilayer (ML) systems. These systems belong to three different regimes of magnetic anisotropy that vary with Co thickness (t C o ): in-plane (sample 1, t C o = 0.74 nm), weakly out-of-plane (sample 2, t C o = 0.6 nm), and out-of-plane (sample 3, t C o = 0.40 nm). Interestingly, we observed that the precession amplitudes increase significantly with decreasing the Co layer thickness. In this study, the influence of various spin dynamics and static magneto-optical parameters on precession amplitude is examined critically and compared with a previously proposed analytical expression that connects those quantities. It is found that the enhancement of structural-dependent energy transfer efficiency between charge and spin subsystems is indeed responsible for the observed variations in precession amplitudes. On the basis of this fact, we discuss that the spin–orbit interaction that yields perpendicularly spin-polarized electrons in the MLs through the Co/Pd interface is responsible for the observed increase in precession amplitudes of locally excited magnetization. Our approach of employing low-fluence laser excitation of magnetization precession could be practical for developing a non-thermal, all-optical magnetic switching toward photonic memory applications. [ABSTRACT FROM AUTHOR]

We investigate the electronic structure and spin-dependent densities of low-energy electron states in a (112) oriented Cd 3 As 2 film. We find that the thick Cd 3 As 2 film is a semi-Dirac material whose dispersion is linear (massless) in one direction and is quadratic (massive) in the orthogonal direction. Its spin-up and spin-down densities corresponding to linear dispersion, respectively, distribute at the top and bottom surface of the film, exhibiting the chirality of Dirac electrons, while the ones corresponding to quadratic dispersion overlap each other. In particular, an appropriate electric field vertical to the top surface of the film can result in anisotropic Rashba spin–orbit coupling and open a bandgap in the quadratic dispersions and its adjacent linear dispersions, driving a topological phase transition from a semi-Dirac-point phase to a Dirac-node-arc phase. Our findings predict a (112) oriented Cd 3 As 2 film to be a candidate semi-Dirac material and provide a method to find Dirac-node-arc states for experiments. [ABSTRACT FROM AUTHOR]

Using density functional theory calculation and rigid band model, we investigate the electronic structure and magnetostrictive properties of transition heavy-metal doped Fe-based (Fe–Al, Fe–Si, Fe–B, and Fe–Be) alloys. It is found that a small amount of addition of 4d/5d heavy-metal atoms greatly enhances the coefficient of tetragonal magnetostriction of Fe-based alloys, reaching up to about 1000 ppm in Fe87.5Al6.25Pt6.25 and Fe75Al18.75Rh6.25 alloys. The underlying mechanism is mainly ascribed to combined factors of band narrowing induced by non-bonded states in pure Fe layer, strong spin–orbit coupling effect by heavy metals, and improved mechanical properties, through analysis of the electronic density of states near Fermi level and k-mesh resolved magnetocrystalline anisotropy energy in momentum space. These results provide useful guidance for optimizing the magnetostrictive performance of Fe-based alloys for practical application. [ABSTRACT FROM AUTHOR]

The spin-pumping behavior in the as-deposited and post-deposition annealed (at 400 °C) Co60Fe20B20/Molybdenum (CoFeB/Mo) heterostructures is investigated. It is found that while in both the as-deposited and annealed CoFeB/Mo heterostructures, Mo crystallizes in the form of mixed phases, i.e., body centered cubic (bcc) and face centered cubic (fcc), the dominance, however, changes from fcc to bcc on annealing. The ferromagnetic resonance measurements reveal that despite relatively low spin orbit coupling of Mo, the spin-pumping efficiency and magnetic properties in both the as-deposited as well as in the annealed heterostructures was comparable with those reported in similar CoFeB based heterostructures comprising of other nonmagnetic metals such as W and Ta. The spin efficiency parameters are, however, slightly better when the Mo film is predominantly in the fcc phase as compared to the case when the Mo film dominantly comprises of the bcc phase. The different spin-pumping efficiencies in the two different combinations of phases of Mo are attributed to the different band structures and the density of states in different phases of Mo, as confirmed by density functional theory calculations. The slight changes observed in the spin-pumping response are possibly attributed to the structural manifestations that result at the interface that the two phases of Mo share with CoFeB. Importantly, despite the weak spin–orbit interaction, the 4d transition metal Mo could be a suitable choice of non-magnetic material for spin pumping when the thermal stability of different layers in the CoFeB based spintronic devices is of paramount concern. [ABSTRACT FROM AUTHOR]

While it is known that a resonant amplification of T c in two-gap superconductors can be driven by using the Fano–Feshbach resonance tuning the chemical potential near a Lifshitz transition, little is known on tuning the T c resonance by cooperative interplay of the Rashba spin–orbit coupling (RSOC) joint with phonon mediated (e-ph) pairing at selected k-space spots. Here, we present first-principles quantum calculation of superconductivity in an artificial heterostructure of metallic quantum wells with 3 nm period where quantum size effects give two-gap superconductivity with RSOC controlled by the internal electric field at the interface between the nanoscale metallic layers intercalated by insulating spacer layers. The key results of this work show that fundamental quantum mechanics effects including RSCO at the nanoscale [Mazziotti et al., Phys. Rev. B, 103, 024523 (2021)] provide key tools in applied physics for quantitative material design of unconventional high temperature superconductors at ambient pressure. We discuss the superconducting domes where T c is a function of either the Lifshitz parameter (η) measuring the distance from the topological Lifshitz transition for the appearing of a new small Fermi surface due to quantum size effects with finite spin–orbit coupling and the variable e-ph coupling g in the appearing second Fermi surface linked with the energy softening of the cut off ω 0. [ABSTRACT FROM AUTHOR]

We investigate the spin Hall effect in a single-layer graphene device with disorder and interface-induced spin–orbit coupling. Our graphene device is connected to four semi-infinite leads that are embedded in a Landauer–Büttiker setup for quantum transport. We show that the spin Hall angle of graphene devices exhibits mesoscopic fluctuations that are similar to metal devices. Furthermore, the product between the maximum spin Hall angle deviation and dimensionless longitudinal conductivity follows a universal relationship Θ s H × σ = 0.18. Finally, we compare the universal relation with recent experimental data and numerically exact real-space simulations from the tight-binding model. [ABSTRACT FROM AUTHOR]

Here, we have presented the results of the detailed theoretical study of thermoelectric properties of two Rashba compounds KSnSb and KSnBi using first principles calculations based on density functional theory and Boltzmann transport theory taking spin–orbit coupling (SOC) into account. As these compounds have layered-type crystal structures, their transport parameters are found to be highly anisotropic. For KSnBi (KSnSb), the calculated lattice thermal conductivity κ l along its crystallographic c axis is found to have ultralow value of 0.49 W m−1 K−1 (0.78 W m−1 K−1) even at room temperature, whereas almost twofold larger value of κ l is estimated along its crystallographic a axis. However, large values of other transport parameters like electrical conductivity σ and thermopower S desirable for a high power factor (S 2 σ) are found along the a axis of these compounds. For KSnSb, the optimum a axis Z T = 2.6 can be reachable for an electron concentration of 3.3 × 1019 cm−3 and at a temperature of 800 K. Comparable value of optimum a axis Z T = 2.5 is also noted for KSnBi despite its strong susceptibility to bipolar conduction. Both these non-centrosymmetric compounds exhibit SOC-driven Rashba spin splitting of electronic bands, which affects both thermopower and electrical conductivity of these compounds. However, such Rashba spin splitting induced change in thermopower is almost negated by the concomitant change in electrical conductivity, resulting in no appreciable impact on power factor and hence Z T of the studied compounds. [ABSTRACT FROM AUTHOR]

Materials with high spin–orbit coupling (SOC) are a prerequisite for the realization of spin–orbit torque-based magnetic memories. Transition metal dichalcogenides (TMDs) are an apt choice for such applications due to their high SOC strength. In this work, we have investigated the spin pumping phenomenon at the interface between thin tungsten disulphide (WS2) films and Co2FeAl (CFA) Heusler alloy films by performing ferromagnetic resonance (FMR) measurements on WS2/CFA heterostructures capped with the 4 nm thin Al film. While Raman spectroscopy conclusively proves the number of monolayers in the WS2 films, atomic force microscopy and x-ray reflectivity measurements were used to quantify the smoothness of the grown interfaces (<0.4 nm) as well as the individual layer thicknesses in the heterostructure stacks. Here, we vary the WS2 layer numbers and CFA thicknesses to quantify the spin pumping parameters such as spin mixing conductance, and spin transparency. FMR measurements revealed that damping enhancement reached ∼41% with a monolayer of WS2. Interfacial effective spin mixing conductance and spin transparency of the WS2/CFA interface are found to be 7.47 ± 0.97 nm−2 and 73.35 ± 9.52%, respectively. Thus, high-quality TMDs can be used as efficient materials for magnetic memory device applications. [ABSTRACT FROM AUTHOR]

The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel's original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel's derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin–orbit coupling. [ABSTRACT FROM AUTHOR]

Using the first-principles method based on density functional theory, we investigate the electronic, mechanical, phononic, superconducting, and topological properties of the A15 superconductor Ti 3 Sb with/without the inclusion of spin–orbit coupling (SOC). We find that the calculated elastic constants satisfy the Born stability criteria and the ductile nature of Ti 3 Sb. The result of phonon calculations reveals that the P m 3 ¯ n structure is dynamically stable. Sb atoms are dominated in the low-frequency region due to the mass difference between Ti and Sb from partial phonon calculations. Our electronic structure calculations show that Ti 3 Sb has metallic band structures with Ti- d bands near the Fermi energy. The electron–phonon coupling constant (λ ≃ 0.80) indicates that Ti 3 Sb has strong electron–phonon coupling. The critical temperature (T c μ ⋆ = 0.10 ) is found to be 6.24 and 6.56 K with and without the SOC effect, respectively. Due to Ti's relatively small SOC strength, we do not find evidence of non-trivial topology in contrast to Ta compounds such as Ta 3 Sb. [ABSTRACT FROM AUTHOR]

The aim of this Tutorial is to give a pedagogical introduction into realizations of Majorana fermions, usually termed as Majorana bound states (MBSs), in condensed matter systems with magnetic textures. We begin by considering the Kitaev chain model of "spinless" fermions and show how two "half" fermions can appear at chain ends due to interactions. By considering this model and its two-dimensional generalization, we emphasize intricate relation between topological superconductivity and possible realizations of MBS. We further discuss how "spinless" fermions can be realized in more physical systems, e.g., by employing the spin-momentum locking. Next, we demonstrate how magnetic textures can be used to induce synthetic or fictitious spin–orbit interactions, and, thus, stabilize MBS. We describe a general approach that works for arbitrary textures and apply it to skyrmions. We show how MBS can be stabilized by elongated skyrmions, certain higher order skyrmions, and chains of skyrmions. We also discuss how braiding operations can be performed with MBS stabilized on magnetic skyrmions. This Tutorial is aimed at students at the graduate level. [ABSTRACT FROM AUTHOR]

M n 2 Au is a bimetallic antiferromagnetic with an extraordinarily high Néel temperature of 1600 K. M n 2 Au has also been found to demonstrate Néel-order spin–orbit torque, allowing for electrical switching of the antiferromagnetic Néel vector. This has led to much interest in this material for spintronic applications. Here, we detail the growth of high quality M n 2 Au (110) thin films. The films were grown on a high quality Pt (111) buffer layer, which was grown on an A l 2 O 3 (0001) substrate. The M n 2 Au films have excellent crystalline quality as demonstrated by x-ray diffraction, x-ray reflection, and reflection high energy electron diffraction measurements. The M n 2 Au (110) films are found to grow with three equivalent in-plane rotation domains, caused by the Pt/ A l 2 O 3 substrate. [ABSTRACT FROM AUTHOR]

The current-induced magnetization switching (CIMS) was successfully observed in epitaxial L10-FePt/CrxPt1−x (0 ≤ x ≤ 1) heterostructures grown by molecular beam epitaxy with large perpendicular magnetic anisotropy. With increasing Cr content, the critical switching current density (Jc) in FePt/CrxPt1−x heterostructures exhibited a decreasing trend, where it was greatly reduced by 69% in FePt/Cr (3d) films compared to FePt/Pt (5d) films with strong spin–orbit coupling. Furthermore, the same switching polarities were observed for all FePt/CrxPt1−x samples, indicating that the orbital Hall effect played a dominant role in CIMS for FePt/Cr films because of opposite spin Hall angles for Cr and Pt. Our results will put forward the applications of L10-FePt in collaboration with the orbital Hall effect from 3d metals in current-controlled magnetic random access memory and neuromorphic computing. [ABSTRACT FROM AUTHOR]

We present detailed investigations of the magnetic properties of Pt/CoFeB/MgO layers as studied using the angle-resolved spin-torque ferromagnetic resonance method. Although the measurements provide reasonable magnetic parameters, we obtain an unusual value in the interfacial spin transparency if spin-pumping is assumed to be the dominant source for enhancing magnetic damping (αeff) in the nanometer thickness regime. However, the thickness dependence of the Landé g-factor (geff) for CoFeB indicates that the interfacial spin–orbit coupling plays a role in determining αeff. In addition, the azimuthal asymmetry in the magnetic system may not be related to the possibility of generating unconventional spin polarization. The results in this work are expected to aid in understanding various magnetic properties and current-induced spin-torques in a heavy-metal/ferromagnet bilayer. [ABSTRACT FROM AUTHOR]

Recent advancement in the switching of perpendicular magnetic tunnel junctions with an electric field has been a milestone for realizing ultra-low energy memory and computing devices. To integrate with current spin-transfer torque-magnetic tunnel junction and spin–orbit torque-magnetic tunnel junction devices, the typical linear fJ/V m range voltage controlled magnetic anisotropy (VCMA) needs to be significantly enhanced with approaches that include new materials or stack engineering. A possible bidirectional and 1.1 pJ/V m VCMA effect has been predicted by using heavily electron-depleted Fe/MgO interfaces. To improve upon existing VCMA technology, we have proposed inserting high work function materials underneath the magnetic layer. This will deplete electrons from the magnetic layer biasing the gating window into the electron-depleted regime, where the pJ/V m and bidirectional VCMA effect was predicted. We have demonstrated tunable control of the Ta/Pd(x)/Ta underlayer's work function. By varying the Pd thickness (x) from 0 to 10 nm, we have observed a tunable change in the Ta layer's work function from 4.32 to 4.90 eV. To investigate the extent of the electron depletion as a function of the Pd thickness in the underlayer, we have performed DFT calculations on supercells of Ta/Pd(x)/Ta/CoFe/MgO, which demonstrate that electron depletion will not be fully screened at the CoFe/MgO interface. Gated pillar devices with Hall cross geometries were fabricated and tested to extract the anisotropy change as a function of applied gate voltage for samples with various Pd thicknesses. The electron-depleted Pd samples show three to six times VCMA improvement compared to the electron accumulated Ta control sample. [ABSTRACT FROM AUTHOR]

A key element to tailor the properties of magnetic multilayers is the coupling between the individual magnetic layers. In the case of skyrmion hosting multilayers, coupling of skyrmions across the magnetic layers is highly desirable. Here, the magnetic interlayer coupling was studied in epitaxial all-oxide heterostructures of ferromagnetic perovskite SrRuO 3 layers separated by spacers of the strong spin–orbit coupling oxide SrIrO 3. This combination of oxide layers is being discussed as a potential candidate system to host Néel skyrmions. First order reversal curve (FORC) measurements were performed in order to distinguish between magnetic switching processes of the individual layers and to disentangle the signal of soft magnetic impurities from the sample signal. Additionally, FORC investigations enabled us to determine whether the coupling between the magnetic layers is ferromagnetic or antiferromagnetic. The observed interlayer coupling strength was very weak for the heterostructure with a two monolayer (ML) thick SrIrO 3 spacer, and no coupling was observed for spacers of 6 and 12 ML thickness. The decoupling of the magnetic SrRuO 3 layers due to the SrIrO 3 spacer is a disadvantage for the study of skyrmions in such multilayers and indicates that other oxides have to be identified for realizing strong magnetic coupling. [ABSTRACT FROM AUTHOR]

The strong spin–orbit coupling (SOC) in lead halide perovskites, when inversion symmetry is lifted, has provided opportunities for investigating the Rashba effect in these systems. Moreover, the strong orbital moment, which, in turn, impacts the spin-pair in singlet and triplet electronic states, plays a significant role in enhancing the optoelectronic properties in the presence of external magnetic fields in lead halide perovskites. Here, we investigate the effect of weak magnetic fields (<1 T) on the photoluminescence (PL) properties of CsPbBr 3 nanocrystals with and without Ruddlesden–Popper (RP) faults and single crystals of CH 3 NH 3 PbBr 3. Along with an enhancement in the PL intensity as a function of an external magnetic field, which is observed in both lead bromide perovskites, the PL emission red-shifts in CsPbBr 3 nanocrystals. Density-functional theory calculations of the electronic band-edge in CsPbBr 3 show almost no change in the energy gap as a function of the external magnetic field. The experimental results, thus, suggest the role of mixing of the triplet and singlet excitonic states under weak magnetic fields. This is further deduced from an enhancement in PL lifetimes as a function of the field in CsPbBr 3. In CH 3 NH 3 PbBr 3 , an increase in PL intensity is observed under weak magnetic fields; however, no changes in the peak energy or PL lifetimes are observed. The internal magnetic fields due to SOC are characterized for all three samples and found to be the highest for CsPbBr 3 nanocrystals with RP faults. [ABSTRACT FROM AUTHOR]